Emission properties of Ti-DLC films prepared by unbalanced magnetron sputtering H.F. Liang a,b , Z.H. Liang b, *, C.L. Liu b , L.G. Meng b a Key Laboratory for Optical Measurement and Thin Films of the Shannxi Province, Xi’an Technological University, Xi’an 710032, China b Key Laboratory for Physical Electronics and Devices of the Ministry of Education, Xi’an Jiaotong University, Xi’an 710049, China 1. Introduction Carbon materials such as amorphous carbon films, diamond- like carbon (DLC) films, diamond films and carbon nanotubes are all recognized as promising candidates for field emission because of their low work function and negative electron affinity. DLC films show better emission properties when doped, so much effort has been expended developing both undoped DLC films and N- [1,2,3,4], B- [5,6], Si- [7] and S- [8] doped DLC films to improve their field emission properties. Furthermore, the effects of film stress and the type of interlayer and substrate on the field emission have also been investigated [9,10]. There is some controversy over the electron emission mechanism in DLC films. A theory for the emission mechanism of DLC films supported by an energy band diagram and emission structures is given in [11]. Other researchers have suggested that emission from DLC films is caused by hot electrons, which are created in the region of strong band bending on the rear contact. This means the carbon-based films only show a low work function when layered on silicon, so silicon is the true cathode [12]. However, the valence band energy of the DLC films measured from their photoemission did not show the presence of substantial band bending on the rear contact [13]. Also, measure- ments of the electron energy distribution did not show hot electrons with high-energy tails [14]. Several results have shown that emission is controlled by a relatively high-energy barrier on the surface of the DLC film [15]. DLC films can emit electrons under a low macroscopic electric field because DLC is an electrically nanostructured heterogeneous material [16,17]. Doped DLC films with excellent emission properties are needed to understand the effects of different dopants on the field emission properties of the resulting films. The field emission mechanism of doped DLC films also requires further clarification. In this paper, we prepared Ti-doped DLC (Ti-DLC) films as field emitters in devices with diode and coplanar structures to investigate their electron emission properties and electron emission mechanism. 2. Experimental Ti-DLC films were prepared on an n-type silicon substrate with 30–40 mV cm resistivity at the base pressure of 2.0  10 3 Pa by a DC magnetron sputtering method. Argon gas was injected into chamber with a flow rate of 100 sccm at a work pressure of 0.8 Pa to sputter the composite target which is composed of Ti (99.9% purity) and C (99.99% purity) layers, as shown in Fig. 1. The sputtering power, bias voltage and target current were maintained at 700 W, 50 V and 1.5 A, respectively. The distance between the composite target and substrate was fixed at 15 cm. A current of Applied Surface Science 256 (2010) 1951–1954 ARTICLE INFO Article history: Received 17 March 2009 Received in revised form 15 October 2009 Accepted 16 October 2009 Available online 24 October 2009 PACS: 85.45.Db 85.45.Bz Keywords: Ti-DLC films Field emission Device structures ABSTRACT The field emission properties of Ti-DLC films in diode and coplanar device structures were studied. An emission current density of 1.14 A/cm 2 could be obtained at an applied field of 33 V/mm and the threshold field was 24 V/mm for the coplanar emission structure. The silicon substrate was found to limit the emission current in the diode structure because of its high resistivity. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +86 029 82663835; fax: +86 029 82669555. E-mail addresses: zhihuliang@126.com, hfliang2004@163.com (Z.H. Liang). Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc 0169-4332/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2009.10.043